The invention relates to a brake device, in particular to a disc or drum brake, having a brake caliper or a brake drum and an energy accumulator, in particular an accumulator spring. The energy accumulator is supported, on the one hand, on the brake caliper or the like, and, on the other hand, by way of a lever arm on an abutment.
A wide and diverse variety of brake devices are known from the prior art, such as, also, vehicle brakes having an elastic energy accumulator, typically a spring accumulator, in which an equilibrium between the energy accumulator and the brake mechanism to be spread open is maintained by adapting the force step-up ratio in the range of possible tension forces of the brake.
Solutions of this type have been adopted, for example, in WO 01/44 677 A1 and WO 03/016745 A2.
A basic illustration of such prior art is shown in FIG. 1.
According to this design, in each position of a displaceable abutment “A”, a stable equilibrium state between the energy accumulator and brake caliper is established by relaxing or tensioning the spring elasticities of the energy accumulator (lever arm l1) and brake caliper (lever arm l2) according to the ratio of the lever arm lengths l1 and l2 and of the spring rigidities c1 and c2.
By displacing the position of the abutment “A”, the tension force of the brake can thus be varied within given limits.
What the solutions of the prior art have in common is that an adjustably positioned abutment is required, in each case, in order to variably set the equilibrium state.
The adjusting operation in this case entails an appreciable outlay in terms of energy, since, depending on the compression state of the energy-emitting or energy-absorbing elements, forces directed opposite to the adjusting movement occur on the adjusting mechanism of the abutment:FA=(F1+F2)·sin φ
There are, in addition, the frictional losses occurring in the adjusting mechanism (see the basic diagram of FIG. 2).
A further problem of the known solutions is that no measures are provided for adapting the force step-up ratios to the spring rigidities of the brake mechanism which are variable due to wear.
Particularly in disc brakes, however, the overall rigidity of the brake mechanism consisting of the brake caliper, the brake pads and the brake disc is influenced substantially by the relatively soft brake lining material.
Since, during operation, the lining material is worn away from a maximum thickness (when new) to virtually zero, a high wear-dependent variation in the overall rigidity of this arrangement occurs.
What is applicable is:
      1          c      overall        =            1              c        Caliper              +          1              c        Lining              +          1              c        Disk            
The amount of coverall may vary, for example, in a ratio of
            c              overall        ·        max                    c              overall        ·        min              =  2as a result of the wear-dependent compressibility of the brake pads.
The result of the pronounced spread in the Coverall value is that, in the extreme states of “lining new” and/or “lining worn”, energy compensation between the energy accumulator and the brake caliper becomes out of tune such that only a small fraction of the possible energy saving is utilized, that is to say, a considerable power consumption of the brake is required, thus making it necessary to have a correspondingly large dimensioning of the electric drive motor and of the following drive elements.
Against this background, the object of the invention is to develop further a brake device such that the problems of the adjustable abutment and, preferably, also the above-described problem of the influence of the lining compressibility, variable as a function of wear, on the power requirement of the brake are in any event essentially eliminated.
According to the invention, a brake device is provided, in particular a disc brake, having a brake caliper and an energy accumulator. The energy accumulator, in particular, an accumulator spring, is supported, on the one hand, on the caliper and, on the other hand, by way of a lever arm on an abutment. A mechanism for transmitting resilient forces between the energy accumulator embodying one spring element and the caliper embodying another spring element is formed with another lever arm via the abutment. The lever arms can take at least two or more different angular positions relative to each other in relation to the abutment.
Accordingly, the lever arms (l1 and l2) can assume at least two or more different angular positions in relation to one another with respect to the abutment “A”. By virtue of this measure, the brake device is provided with a force step-up mechanism which, in the case of a suitable arrangement of the force action directions of the accumulator spring and brake caliper tension force in relation to the lever arms acted upon by these forces, and also of the configuration of the lever arm lengths and rigidities of the two spring systems in relation to one another, is automatically in an equilibrium state in any adjustment position of the lever and, therefore, in the case of any tension force of the brake which is to be set.
The simple design of the lever system, in conjunction with its special properties, makes it possible in this case to adapt the step-up characteristic to the caliper rigidity variable as a function of wear.
This is implemented preferably in that the lever arm generating the tension force is held variably in its angular position in relation to the force direction of the tension force.
Thus, in turn, preferably an angular position of the other lever leading with respect to the angular position of one lever arm is set. This lead angle is increased proportionally to the brake lining wear preferably by the action of the wear adjustment system present in the brake. In this way, the increasing rigidity of the brake caliper is compensated by a continuous increase in the step-up ratio and an adapted progression of the step-up.
The invention also provides a disc brake having a caliper which straddles a brake disc, for example, in a frame-like manner, there being arranged as an energy accumulator in the caliper an accumulator spring, which is supported with one of its ends via a support bearing on the inside of the caliper or of a spring pot in the region facing away from the brake disc, the end which faces the brake disc or the front region of the accumulator spring being articulated at a joint as an articulation point, preferably on a brake lever pivotable by an adjusting mechanism. This type of construction makes it possible to have a structurally perfectly cost-effective and simple implementation of the brake device according to the invention as a disc brake.